Integrated circuits are used in many electronic devices. A typical integrated circuit includes a semiconductor substrate, such as formed of silicon. A number of active regions may be formed in the substrate, and a plurality of interconnect layers are formed on the substrate to interconnect the active regions and/or facilitate external connections to the active regions. Typically a plurality of integrated circuits are collectively formed on a semiconductor wafer.
It is also typically important to planarize the wafer after various process steps to remove unwanted portions or to ensure a planar upper surface for forming a next layer thereon. One common technique to planarize a wafer is known as chemical mechanical polishing (CMP). CMP is very widely used technique which delivers a slurry of material to the wafer surface and while a polishing pad or belt is passed over the wafer surface. For example, U.S. Pat. No. 4,972,432 entitled "Pad Material for Grinding, Lapping and Polishing" discloses a polishing pad including a porous thermoplastic resin matrix, such as comprising polyurethane, reinforced with a fibrous network provided by a felted mat of polyester fibers. The polishing material is modified by coalescing the resin among the fibers, preferably by heat treatment, to increase the porosity and hardness of the material as well as increasing the surface activity of the resin. The two different resins have different melting temperatures so that one is coalesced first. The polishing material may also incorporate polishing aids, such as particulate abrasives.
Another polishing pad is disclosed in U.S. Pat. No. 5,578,362 to Reinhardt et al. This patent discloses in its background a number of different pad constructions including a so-called "minitexturized" pad which includes intermediately sized textured artifacts on the pad, which may be produced by use of lasers or the incorporation of air or gas within the pad material. Conventional pads are described as including "microtexture" which is the intrinsic microscopic bulk texture of the pad after manufacture which is largely random. "Macrotextures" are artifacts or features generally greater than about 5 mm, and spacing and sizes are typically very regular and repetitive. The patent further discloses a pad including a plurality of microelements impregnated into a polymeric matrix. The polymeric microelements at the work surface are less rigid than those embedded. Accordingly, the less rigid microelements at the work surface cause the surface of the pad to be continuously regenerated.
U.S. Pat. No. 5,584,146 to Shamouillan et al. discloses a polishing pad including a plurality of conduits passing through the entire thickness of the pad. The conduits are to hold the slurry uniformly across the surface of the polishing pad, and to permit the addition of slurry or other materials therethrough.
Rodel, Inc. of Newark, Del. makes a line of CMP pads formed from filled and/or blown urethanes such as IC-series, MH-series and LP-series polishing pads. These have a surface structure made up of semicircular depressions derived from the cross-section of exposed hollow spherical elements or incorporated gas bubbles.
Despite continuing advances in the area of pads for CMP, there still exists a need for pads having more uniform surfaces, especially as the pad wears. In addition, the purity of such pads is desirably controlled to produce more consistent polishing results.